Needles are used in a variety of applications. Medical, surgical and cosmetic needles are broadly used to penetrate into a human or animal body. Metal and metal alloys, especially stainless steel, has been for several decades the material of choice for needles.
Stainless steel needles have been appreciated for their high compression and flexural strength, high rigidity, high stiffness, high surface hardness, high ductility, high impact resistance, high chemical resistance, high corrosion resistance, non combustibility, low moisture absorption, good ability to hold a sharp edge and penetrability.
The penetrability of a needle can be defined as the ability or easiness for a needle to penetrate in a suitable manner into a substrate such as a skin or a vein; upon penetration, the needle should neither break nor endorse a substantial deformation; it should not tear up in any manner the substrate that is penetrated (esp. it should not rip up the flesh). Further, needles for injection into human or animal tissue have to be terminated by a sharp edge (also named, point) and to be very small in diameter in order to limit the pain experienced by the patient, whilst retaining adequate penetrability of the skin, vein, muscle or the like.
As the skilled person will easily understand, this property is key for a needle and is essentially specific to this end use. Insofar as the Applicant knows, it is extremely difficult to predict what the penetrability of a needle is based on more familiar properties of the material the needle is made of Besides, without being bound to any theory, the Applicant is of the opinion that achieving the right penetrability likely requires a subtle and unelucidated balance of properties, among which it could possibly be cited a.o. high compression and flexural strength and high rigidity on one hand, and high ductility and a high impact resistance on the other hand; the penetrability depends further on the design of needle, including its length, aspect ratio and, last but not least, the sharpness of its edge.
With this regard, the ability to hold a sharp edge is another key property for a needle. Indeed, this property does not only improve the penetrability of the needle as above explained, but it also contributes as such to decrease or relieve the pain felt by a patient (or more generally by a human or an animal) when the needle penetrates and possibly goes through its skin, vein, muscle or other surface layer. As the skilled person will easily appreciate, it is also essentially specific to needle end uses. The Applicant is not aware of any study that would have addressed so far the question of the ability for a needle to hold a sharp edge as function of the chemical nature of the plastic material the needle would have been made of. Finally, to the best of the Applicant's knowledge, it is also extremely difficult to predict the ability of a needle to hold a sharp edge, relying on more familiar properties of the material the needle is made of. Finally, without being bound to any theory, the Applicant is of the opinion that the ability for a needle to hold a sharp edge likely requires a complex and obscure balance of properties, among which it could possibly be cited a.o. a high compression and flexural strength and a high rigidity on one hand, and a high stiffness and a high surface hardness on the other hand; it depends further on the machinability of the material the needle is made of, in particular of the melt processability of the plastic material in case of plastic needles.
Because of this confluence of properties, the needles of the prior art have been generally made of metal. However, metal needles, once they have been used, cannot be easily disposed of, and this gives rise to a sanitary health problem because of contamination accidents arising from contact with or accidental re-utilization of thereof. Indeed, while a needle, such as a medical, surgical or cosmetic needle, can be manufactured under sterile and apyrogenic conditions, and can be kept sterile and apyrogenic in its original pack, once it has been taken out from its pack and utilized, it cannot obviously be held anymore as sterile and apyrogenic.
There is a strong need for single-use, easily disposable needles. This need is immediately apparent when thinking about applications such as mass vaccinations in Third-World countries which are not or poorly equipped with facilities allowing for re-sterilizing or depyrogenizing hypodermic needles that have already been used. Also, even in countries equipped with such facilities, re-sterilization and depyrogenization remain a tedious, time-consuming and complex processes, and, in general, it is also difficult to find reconditioning installations that would provide the same level of health safety as high as those offered by those achieving the original conditioning of the needles.
Another problem commonly associated with metal needles results in the rather poor machinability of the metal, which problem is particularly acute when needles terminated by an extremely sharp edge have to be machined, as required by certain applications in the medical field or as it is the case with single tattoo needles.
There is thus also a need for needles which can be machined more easily, including when the needles have an extremely sharp edge.
In order to solve the problem of providing single-use, easily disposable, easily machinable needles suitable for penetrating into the human body and able to hold a sharp edge, needles made of certain plastic materials have been proposed.
JP 7 303 700, the whole content of which is herein incorporated by reference for all purposes, describes a synthetic resin needle reinforced with combustible fibers whose longitudinal directions are arrayed straight or curvilinearly along the axial length of the needle. JP'700 proposes a wide variety of resins for making the reinforced synthetic needle. According to JP'700, the resin can be notably a thermoplastic resin, such as a polyphenylene sulfide, a polyetheretherketone, a polybutyleneterephthalate, a polycarbonate, a polyamide, a polyacetal, a modified polyphenylene ether, a polyester system resin, a polytetrafluoroethylene, a fluororesin, a polysulfone, a polyetherimide, a polyethersulfone, a polyetherketone, a polyetherlactone, a liquid crystal polyester, a polyamideimide, a polyimide or a polyethernitrile, a polypropylene, a polyethylene or a cyclic olefin system resin; it can also be a thermoset resin such as an epoxy resin, an unsaturated polyester resin, a phenol resin, a urea resin, a melamine resin or a polyurethane resin.
US 2004/199127, the whole content of which is herein incorporated by reference, describes a process for the manufacture of a plastic injection needle in which the employed plastic is a liquid crystalline polyester comprising 70-80 percent hydroxybenzoic acid and 20-30 percent hydroxynaphthoic acid. The plastic needle of US 2004/199127 preferably further comprises from 15 to 40 percent by weight of the solid plastic of fiber reinforcement such as glass fiber or carbon fiber or aramid fiber.
While easily disposable, the needles U.S. Pat. No. '127 which are made of unreinforced liquid crystalline polyester have not the suitable confluence of properties achieved by metal needles, lacking notably in compression and flexural strength, rigidity, penetrability and ability to hold a sharp edge. By the way, exactly the same drawbacks would apply to needles that would have been made of unreinforced polymer material based on any of the synthetic resins described in JP'700, in particular based on polyetheretherketone (PEEK).
Likewise, the needles U.S. Pat. No. '127 which are made of reinforced liquid crystalline polyester and, more generally, the needles of JP'700 which can be made of a variety of other reinforced synthetic resins, have not the suitable confluence of properties achieved by metal needles, lacking notably in ductility, impact resistance, penetrability and ability to hold a sharp edge; the reinforcing agent present in the synthetic resin matrix limits also substantially the possibilities of subsequent recycling of the polyester material.
US 2007/073249, the whole content of which is herein incorporated by reference, describes a needle constituted of a cylindrical body extended along a longitudinal axis, said body being made of a polyaryletherketone polymer (such as PEEK) and further comprising metal reinforcement wires embedded in the polyaryletherketone polymer, extending parallel to the longitudinal axis and distributed according to a particular design. The composite needle of U.S. Pat. No. '249 is not easily disposable because of the metal reinforcement wires embedded in the polymer matrix. The composite needle of U.S. Pat. No. '249 is more difficult to manufacture than a simple plastic or a metal needle. In addition, meeting a suitable confluence of properties with such a composite needle requires also more subtle adjustments, depending further notably on amount, dimensions, shape and positioning of the metal wires.
There are still other reasons making it extremely difficult to find a plastic material that could suitably replace metal for numbers of needle applications.
Firstly, needles are typically small in diameter, and hollow needles have typically very thin walls, which can makes it difficult to mold a plastic material in a standard mold, or to extrude a plastic material through a standard extrusion head/die. Oftentimes, the viscosity of these materials in the die is so high that one must increase the temperature of the polymer in order to reduce the viscosity of the material so that they can get sufficient flow in the orifices of the mold or through the die. This practice can dramatically alter material properties. Hence, plastic materials suitable for making needles must demonstrate a good thermal stability and good melt processability.
Then, needles used to penetrate into a human or animal body, must be non toxic and non irritant. They should not elicit any adverse host reactions to their contact, and, more generally, they should cause no injurious effect on the part of the body the are put in contact with. This further requires the plastic material to demonstrate excellent biocompatibility features.
There is a need for needles, in particular medical and surgical needles, exhibiting a confluence of characteristics including high compression and flexural strength, high rigidity, high stiffness, high surface hardness, high ductility, high impact resistance, high chemical resistance, high corrosion resistance, non combustibility, low moisture absorption.
There is a need for needles having a good penetrability.
There is a need for needles having a good ability to hold a sharp edge.
There is a need for needles that are non toxic. There is a need for needles that are non irritant. There is a need for needles that are biocompatible.
There is a need for easily disposable needles, which would then be especially well suited for a single-use. There is a need for needles made from a material exhibiting a good disposability and recyclability.
There is a need for needles made from an easily machinable material. There is a need for needles made of an easily melt processable and thermally stable material.
The present invention can solve the above problems.